1. Field of the Invention
This invention relates to a method of and an apparatus for permitting deep drawing of a work.
2. Description of the Prior Art
In a process of deep drawing of a work, it is liable that the work is excessively elongated to result in rupture. FIGS. 10(a) and 10(b) show an example of the deep drawing process. As shown, a panel W as a work is clamped between a stationary die 102 and a movable die 104, and it is elongated by lowering a punch 106 as shown by an arrow A. A portion of the work W which has a length lc before the process is elongated to a length lc1 after the process. With increasing drawing of the work, the elongation factor thereof is increased, making the work to be readily ruptured.
A technique which permits deep drawing of a work by preventing the rupture thereof, is disclosed in Japanese Laid-Open Utility Model Publication No. 61-148423. This technique will now be described with reference to FIGS. 9(a) and 9(b). In this technique, a stationary die comprising an immovable part 102b and a movable part 102a are used. The movable part 102a is displaced to the right as shown by an arrow B in synchronism with the descent of a punch 106 as shown by an arrow A. In this case, a portion of the work which has a length of la before the process is elongated to a length of la1 after the process. As is obvious from FIGS. 9(a), 9(b), 10(a) and 10(b), when the lengths la1 and lc1 after the process are equal, the length la before the process in FIG. 9(a) can be set to be greater than the length lc before the process in FIG. 10(a). That is, with the FIGS. 9(a) and 9(b) techniques, the elongation factor of the work can be suppressed much more than in the FIGS. 10(a) and 10(b) technique.
FIG. 7 shows a technique which was developed from the FIG. 9 technique. This technique was studied by the inventors while the present invention was developed. In this technique, a stationary die 111 having a recess 111j formed in the top surface (i.e., processing surface) is used. A movable die 115 is caused to approach the stationary die 111 as shown by a vector P. A movable die part 116 is caused to slide along a slanted surface 115a of the movable die 115 as shown by a vector S. While the movable die 115 approaches the stationary die 111 to an extent as shown by the vector P, the movable die part 116 is caused to slide slantedly along the movable die 115 to an extent as shown by the vector S. Reference numeral 112 designates a cushion ring which is biased upward by a pin 113. In FIG. 7, the cushion ring 112 is shown located at an intermediate level. The movable die 115 has a wrinkle restraining part 115x.
In this apparatus, as the movable die 115 approaches the stationary die 111, the work panel W is clamped between the cushion ring 112 and the wrinkle restraining part 115x of the movable die 115. Subsequently, a point A of the movable die part 116 is brought into contact with the work panel W, and eventually, the point A is displaced to a point B as shown by a vector K, thus completing the deep drawing process. The vector K is the vector sum of the vectors P and S. The vectors P and K have different directions.
FIG. 8 shows vector sums K1 to K3 when extent P to which the movable die 115 approaches the stationary die 111 while the movable die part 116 slides by the vector S, is set to P1 to P3, respectively. It will be seen that the greater the extent P the nearer the vertical the vector K is. Shown at A1 to A3 are the positions of contact between the movable die part 16 and the work panel W in the cases when the movable die part 116 is displaced by the vectors K1 to K3, respectively. Shown at C is the upper edge in the deep drawing process, i.e., the edge of the recess 111j on the side of the movable die 115. Obviously, the nearer the vertical the vector K is, the smaller the length before the process, and the nearer the horizontal the vector K is, the greater the length before the process.
As shown, in order to increase the length before the process and thus reduce the elongation factor, the vector K is suitably nearer the horizontal. To this end, the movable die part 116 suitably undergoes a displacement as shown by the vector S with a very small stroke right above the lower dead center of the movable die 115. In other words, the movable die part 116 suitably starts to be displaced when the movable die 115 is brought to a position D3 as shown in FIG. 8 rather than when the movable die 115 is brought to a position D1.